Flutter定义了三种不同类型的Channel，它们分别是
▪ BasicMessageChannel：用于传递字符串和半结构化的信息。
▪ MethodChannel：用于传递方法调用（method invocation）
▪ EventChannel: 用于数据流（event streams）的通信。
原理讲解咸鱼团队的技术文章讲解的很通透了：深入理解Flutter Platform Channel
这篇文章在官方platform_channel的示例基础上，补全了示例子中没有实践的种方式。
Fultter侧实现
BasicMessageChannel
1 创建messageChannel
static const BasicMessageChannel messageChannel =
BasicMessageChannel('samples.flutter.io/message', StandardMessageCodec());
1.1 发送数据到NA flutter -> NA
// result接收异步回调的数据
String parama = await messageChannel.send('flutter 参数');
1.2 接收NA发过来的数据 NA -> flutter
Future<String> messageHandler(parama) async {
print('messageHandler ' + parama);
_naToFlutterText = parama;
return 'messageHandler flutter return';
}
// void setMessageHandler(Future<T> handler(T message))
messageChannel.setMessageHandler(messageHandler);
MethodChannel
2 创建MethodChannel
static const MethodChannel methodChannel = MethodChannel('samples.flutter.io/battery');
2.1 flutter调用NA方法 flutter -> NA
try {
final int result = await methodChannel.invokeMethod('getBatteryLevel');
// 处理成功结果
} on PlatformException {
// 处理异常结果
}
2.2 NA调用flutter方法 NA -> flutter
Future<String> methodHandler (MethodCall call) async {
print(call.method + '-----method');
print(call.arguments + '-----argument');
return '回调结果';
}
// void setMethodCallHandler(Future<dynamic> handler(MethodCall call))
methodChannel.setMethodCallHandler(methodHandler);
EventChannel
3 创建EventChannel
static const EventChannel eventChannel = EventChannel('samples.flutter.io/charging');
3.1 接收NA发送过来的stream NA -> flutter
// Stream<dynamic> receiveBroadcastStream([ dynamic arguments ])
// StreamSubscription<T> listen(void onData(T event), {Function onError, void onDone(), bool cancelOnError});
eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
void _onEvent(Object event) {
// 正常数据流
}
void _onError(Object error) {
// 失败数据流
}
对于 eventChannel.receiveBroadcastStream() 添加多次没有意义，只会有一个生效，添加第二个的时候，会先把前一个cancel掉。
iOS侧实现
1 创建channel
// 创建massageChannel
FlutterBasicMessageChannel *massageChannel = [FlutterBasicMessageChannel messageChannelWithName:@"samples.flutter.io/message" binaryMessenger:controller];
// 创建methodChannel
FlutterMethodChannel *methodChannel = [FlutterMethodChannel
methodChannelWithName:@"samples.flutter.io/battery" binaryMessenger:controller];
// 创建eventChannel 代理方法里处理stream流 delegate设置为self
FlutterEventChannel *eventChannel = [FlutterEventChannel eventChannelWithName:@"samples.flutter.io/charging" binaryMessenger:controller];
[eventChannel setStreamHandler:self];
2 接收flutter发送过来的message和method flutter -> NA
// 接收flutter发过来的message
[self.massageChannel setMessageHandler:^(id _Nullable message, FlutterReply _Nonnull callback) {
NSLog(@"flutter->na message %@ ", message);
callback([NSString stringWithFormat:@"flutter->na message callback %@ ", message]);
}];
// 接收flutter调用的方法
__weak typeof(self) weakSelf = self;
[methodChannel setMethodCallHandler:^(FlutterMethodCall* call,
FlutterResult result) {
if ([@"getBatteryLevel" isEqualToString:call.method]) {
int batteryLevel = [weakSelf getBatteryLevel];
if (batteryLevel == -1) {
result([FlutterError errorWithCode:@"UNAVAILABLE"
message:@"Battery info unavailable"
details:nil]);
} else {
result(@(batteryLevel));
}
} else {
result(FlutterMethodNotImplemented);
}
}];
3 NA发送message和method到flutter NA -> flutter
// na to flutter 发送普通消息
[self.massageChannel sendMessage:@"na message 参数" reply:^(id _Nullable reply) {
NSLog(@"na->flutter message callback %@ ", reply);
}];
// na to flutter 调用flutter方法
[self.methodChannel invokeMethod:@"naCallFlutter" arguments:@"na method 参数" result:^(id _Nullable result) {
NSLog(@"na->flutter method callback %@ ", result);
}];
在NA侧FlutterEventChannel 接收和发送stream流通过协议FlutterStreamHandler进行的，可以方便的进行NA->flutter方向的数据发送，但是从flutter给NA发送呢数据流，dart侧没有提供api。通过StreamController应该是可行的，它的继承关系如下自StreamController<StreamSink<StreamSink<EventSink，查询dart文档，在EventSink 中有
/**
* Adds a data [event] to the sink.
*
* Must not be called on a closed sink.
*/
void add(T event);
不过没有试验成功从flutter数据流到NA侧，在dart侧是可以内部发送数据流的。
Android侧实现
1 创建channel
// 创建massageChannel
BasicMessageChannel channel = new BasicMessageChannel(registrar.messenger(), "flutter_message_plugin", StringCodec.INSTANCE );
channel.setMessageHandler(new BasicMessageChannel.MessageHandler() {
@java.lang.Override
public void onMessage(java.lang.Object object, BasicMessageChannel.Reply reply) { //flutter发送消息到平台测
Log.i("BasicMessageChannel", "接收到Flutter的消息:" + object);
}
});
channel.send("发送消息到Flutter");
// 创建methodChannel
new MethodChannel(getFlutterView(), "samples.flutter.io/battery").setMethodCallHandler(
// 直接 new MethodChannel，然后设置一个Callback来处理Flutter端调用
new MethodCallHandler() {
@Override
public void onMethodCall(MethodCall call, Result result) {
// 在这个回调里处理从Flutter来的调用
if (call.method.equals("getBatteryLevel")) {
int batteryLevel = getBatteryLevel();
//result是给Flutter的返回值
if (batteryLevel != -1) {
result.success(batteryLevel);
} else {
result.error("UNAVAILABLE", "Battery level not available.", null);
}
}
} else {
result.notImplemented();
}
}
});
// 创建eventChannel 代理方法里处理stream流 delegate设置为self
new EventChannel(getFlutterView(), "samples.flutter.io/charging").setStreamHandler(
new StreamHandler() {
// 接收电池广播的BroadcastReceiver。
private BroadcastReceiver chargingStateChangeReceiver;
@Override
// 这个onListen是Flutter端开始监听这个channel时的回调，第二个参数 EventSink是用来传数据的载体。
public void onListen(Object arguments, EventSink events) {
chargingStateChangeReceiver = createChargingStateChangeReceiver(events);
registerReceiver(
chargingStateChangeReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
}
@Override
public void onCancel(Object arguments) {
// 对面不再接收
unregisterReceiver(chargingStateChangeReceiver);
chargingStateChangeReceiver = null;
}
}
);
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